For me, I choosed 16 GB iPhone.
Someone may think 16 GB is not enough because they are hard core storage users. They take many many photos, long lenght videos, use many applications, store ton of songs, and games that use high amount of storage. So, 16 GB will never enough for them.
Those storage uses style are opposite from me. I have only 100+ but not over 200 songs, never take long lenght videos (the longest videos I've taken are never reach 15 minutes), I've used around 10-15 applications on my iPhone. What about games on iPhone? I've downloaded only 2-4 games on my iPhone. When I don't need to play anymore, I always delete it from my iPhone.
From my storage uses style that I explained above. You'll see that 16 GB iPhone is enough for me. At this time when I was writing this blog entry, my 16 GB iPhone had around 6.8 GB free storage that I think it is plenty.